1. Field of the Invention
The present disclosure relates to an inkjet head. In particular, the present disclosure relates to an inkjet head used as a production apparatus.
2. Description of the Related Art
In recent years, there has been a growing demand for larger screens and higher pixel resolution in various displays.
Among those displays, an organic light emitting diode display (in the following, referred to as an OLED display) is produced by either a deposition method of placing a substrate of the display in a vacuum and depositing an organic layer on the substrate or a printing method of applying ink prepared by dissolving a material of the organic layer in a solvent onto pixels of the display under atmospheric pressure. The printing method is more advantageous for production of a large screen display.
The printing method usable for the production of the OLED display includes a plurality of printing techniques. Among these printing techniques, an inkjet technique is appropriate in view of an utilization efficiency of the material.
In order to improve the pixel resolution of the OLED display by the inkjet technique, a high-density inkjet head having a reduced distance between nozzle holes is needed.
The inkjet head includes a piezoelectric element that applies pressure to ink. The piezoelectric element is provided for each of the nozzles.
In order to apply a voltage to each piezoelectric element, a flexible cable including a wire is used. A control device and each of the piezoelectric elements are connected by the flexible cable. The piezoelectric elements are aligned with a fine pitch. Thus, when the flexible cable and the piezoelectric element are poorly connected, adjacent piezoelectric elements are short-circuited, causing a problem of reduced production yields.
Japanese Unexamined Utility Model Registration Application Publication No. 63-90876 discloses a technique illustrated in FIG. 16.
FIG. 16 is a plan view illustrating cable 21 to be connected to a piezoelectric element. Cable 21 includes a plurality of substrate electrodes 23 that are formed adjacent to each other on insulating substrate 22. Furthermore, holes 24 are formed in advance on insulating substrate 22 between tips of substrate electrodes 23. Holes 24 collect excess solder when substrate electrodes 23 are connected to the piezoelectric elements. This prevents a short-circuit between substrate electrodes 23.
Japanese Unexamined Patent Application Publication No. 2002-110269 discloses a technique illustrated in FIG. 17. FIG. 17 is an enlarged perspective view illustrating connector 27.
A plurality of adjacent connector electrodes 25 are provided on insulating substrate 26. Connector 27 further includes recesses 28 that are formed between connector electrodes 25. When connector 27 is soldered to element electrodes of the inkjet head, recesses 28 collect overflowing solder. This prevents a short-circuit between adjacent connector electrodes 25.
When a piezoelectric element including adjacent piezoelectric bodies and a flexible cable including a plurality of adjacent substrate electrodes provided on an insulating substrate are soldered to each other, it is conceivable that excess solder that has overflowed from the substrate electrodes is collected into holes 24 or recesses 28 by forming holes 24 on the insulating substrate as described in Japanese Unexamined Utility Model Registration Application Publication No. 63-90876 or by forming recesses 28 on the insulating substrate as described in Japanese Unexamined Patent Application Publication No. 2002-110269.
However, when the substrate electrode achieves a finer pitch, it is difficult to provide holes 24 or recesses 28 having an effective size on the insulating substrate.
Moreover, when the excess solder enters between the adjacent piezoelectric bodies, it may solidify to form solder chips and cause a short-circuit.